One step forward and two steps back

[johnnydog]

There are some interesting technical articles available on Chris Witors website regarding the head applications for all models, and also the flow rates for the 219016 head.

[Binny]

Hi Alec,

As far as I know PI engines up to MG 50000 had the 516816 head with 32 mm dia exhaust valves. Both my cars are Mk2 with engine numbers in the MG 1800 to 2100 range so think my donor car will have one of those although I’m going to check this afternoon.

[Binny]

I’ve read the info on Chris Witor’s site regarding cylinder heads - it’s very informative, thanks Johnny Dog.

I think I might contact Chris to see if he can point me in the right direction as to which head and valve springs I should use.

[Binny]

I can confirm that the head on my original 71 pi is a 516816 with double valve springs. Also the height of the head is 3.45” which is the same as the 219016 head.

[Binny]

I’ve just heard from Chris Witor and he recommended using the 219016 head but reducing its height to 3.4” and using the double valve spring set up as used on the original pi head.

So it’s off to the machine shop

[Binny]

So an update.

The head has been machined to give a height of 3.4” along with new valve guides and machining of the valve seats. I refitted the head along with all manifolds and ancillaries and I’ve just filled it with coolant with a view to giving the engine an initial start up.

Unfortunately as I was underneath the vehicle draining the engine oil I noticed a small coolant leak. At first I thought it was from one of the core plugs that I’ve just replaced but, after removing the throttle bodies and exhaust manifold again, the leak is coming from the joint between the cylinder head and upper face of head gasket at several places on the drivers side of the engine. Bearing in mind that the coolant is leaking without being under any pressure then it’s pretty concerning.

I torqued the head in the correct order to 75 lbs/ft using a new Payen gasket and the faces of the block and head were spotless. I’ve rechecked the head nut torques and they’re spot on although I’ve noticed that different manuals seem to give differing torque settings.

Anyone have any idea what might be wrong? I don’t think it can be the cylinder head face as it’s just been skimmed and was vacuum checked for any leaks. I’ve also read that Payen gaskets are now made in Belgium and that quality has suffered as a result.

[Alec]

Hello Binny,

little choice but to remove the head again.
My first thought is that the gasket, for whatever reason does not match the coolant transfer holes? That is what I would check first.

Alec

[Binny]

Hi Alec,

The head is already off (how easy is it to work on these engines compared to modern vehicles?) and the gasket matches up perfectly with all the relevant holes.

One thing I did notice was that the gasket didn’t seem to have been compressed at all despite me tightening it to the max torque! The Payen gaskets are composite and have a thin alloy ring round each cylinder with a strengthening piece on one side between cylinders 1 & 2; 3 & 4 and 5 & 6 which is very slightly thicker than the rest of the gasket and there are no witness marks of any compression on these. Also when placing a straight edge across the block face, tight up against the head studs, there is a gap of a few thou under the straight edge in the middle of the block. This gap isn’t there when the straight edge is moved very slightly away from the studs and consequently I’m wondering if the head has been over tightened in the past leading to the area immediately next to the studs being ‘pulled up’ for want of a better expression.

Ideally the solution would be to get the block face skimmed but I haven’t got the appetite to take the engine out at the moment so am thinking that if I remove the head studs and very, very slightly counter bore/counter sink the stud holes in the block and also head then it might remove these high points and allow the head to sit down properly on the block.

My next problem is how to remove the head studs - any suggestions?

[Charles H]

Have you got the correct head gasket? If you have a recessed block gasket on a non recessed engine it will have the symptoms you describe.

[Binny]

Hi Charles,

I ordered a GEG346 non recessed block gasket from Rimmers so it should be correct although they might’ve sent the wrong one - I’ve never seen a recessed block gasket so can’t compare and the gasket that was originally on it was absolutely knackered and came off in twenty pieces.
The thickness of the alloy parts of this Payen gasket is 1.5 mm whilst the thickness of the other material is 1.00 mm - does that sound like a recessed block gasket?
I think I’m going to get a non Payen gasket anyway.